Method of providing quality of service in a mobile telecommunications network

ABSTRACT

In a third generation telecommunications network, quality of service can be provided to a mobile in a foreign network by providing a quality of service session divided into a first section from the correspondent node ( 24 ) to the home network ( 50 ) and a second section from the home network ( 50 ) to the mobile node ( 28 ); a quality of service enquiry message is sent through both sections, but a quality of service response message is not returned in the first section until the response message from the second section has been received by the home network ( 50 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of Great Britain Patent Application No.0020581.5, which was filed on 21^(st) Aug. 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved method of operating a mobiletelecommunications network, especially a method of addressing packetsdestined for a mobile terminal in a foreign network.

2. Description of Related Art

In third generation telecommunications networks such as GPRS (GeneralPacket Radio Service) and EDGE (Enhanced Data-rate for GSM Evolution),when a mobile terminal moves into a foreign network, networkconnectivity is optionally maintained by the use of Mobile InternetProtocol (Mobile IP). In the home network, a Home Agent (HA) is set upwhich maintains the location information of the mobile by use of BindingUpdates, i.e., registration of information sent to the HA by the mobilenode.

Mobile IP has two working modes. The first is illustrated in FIG. 1; amobile terminal is currently attached as Mobile Node (MN) 14 in anetwork different from its home network. The MN 14 is communicating witha Correspondent Node (CN) 12. A Home Agent 16 is set up in the homenetwork by the CN 12, and a Foreign Agent (FA) 18 is set up in theforeign network. The FA 18 allocates a unique IP address for thevisiting mobile, a Care of Address (COA) and this address is sent to theHA 16 in a Binding Update.

Packets for the mobile are encapsulated by the HA 16 and tunnelled alongtunnel 20 to the FA 18 for transmission to MN 14. In such encapsulation,an extra IP header is added to each packet, including the COA of the MN14. This is known as FA-COA working mode.

In the second working mode (not illustrated) there is no FA, the MN 14is allocated a unique COA and encapsulated packets are tunnelled by HA16 directly to MN 14; this is known as Colocated Care of Address mode ofworking (CO-COA).

In both FA-COA and CO-COA modes of working, the encapsulation generatesextra headers, and possibly only small payloads can be used, whichresults in inefficient transmission and inefficient use of expensivesystem and network resources, such as radio links. Further,encapsulation hides the flow identification, and the differentiation ofclasses of services is thus also disabled, so that Quality of Service(QoS) provision mechanisms, such as RSVP (Resource reSerVation Protocol)Int Serve, must be changed.

The disadvantages of encapsulation can be avoided by the use of NonEncapsulation Mobile IP technique, as set out in the applicant'sco-pending patent application “Non-encapsulation Mobile IP” filed on 26Feb. 1999 as no. 99301437.2. In this technique, the current COA of themobile node is used as the destination address, and the original sourceaddress, i.e. the CN address, is maintained. For FA-COA working, thisdeletes a header of length at least 20 bytes and introduces a header ofonly 2 bytes; for CO-COA mode of working no header is introduced.However a disadvantage is that any firewall or egress filtering in thehome network may reject such packets, because they have a source addressdifferent from the home network address.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of packetaddressing which overcomes the disadvantages set out above, and allowsQoS to be provided.

According to the invention, a method of providing quality of service ina third generation mobile telecommunications system, in which packetsare addressed to a mobile node which has a correspondent node in a homenetwork and which is currently associated with a foreign networkcharacterized by the steps of

sending a quality of service enquiry message from the correspondent nodeto the home network;

sending said quality of service enquiry message from the home network tothe mobile node;

sending a quality of service response message from the mobile node tothe home network by the same route as the enquiry message;

and sending a quality of service response message from the home networkto the correspondent node only after receipt of the quality of serviceresponse message from the mobile node.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example only with reference toFIGS. 2 to 4 in which

FIG. 2a illustrates the invention operating in FA COA mode;

FIG. 2b illustrates the invention operating in COCOA mode;

FIG. 3a illustrates a prior art packet header format;

FIG. 3b illustrates a packet header format according to the invention;and

FIG. 4 illustrates a RSVP session.

DETAILED DESCRIPTION

In FIG. 2a, which is similar to FIG. 1, a mobile terminal MN 28 has a FA30. CN 24 has a HA 26; the figure illustrates FA COA mode. In FIG. 2b,the mode is CO-COA, therefore there is no FA and packets pass directlyto MN 28.

It will be seen that, in comparison with FIG. 1, FIGS. 2a and 2 b do nothave a tunnel from HA 26 towards either FA 30 or MN 28. This is becausein the inventive arrangement the packets are not encapsulated andtherefore no tunnel is needed. A suitable name and acronym for theinventive technique is Non-Encapsulation Mobile Internet Protocol,NEMIP.

In FIG. 3a, a packet 30 conventionally addressed to a mobile in aforeign network has as source address 32 the IP address of CN 24; and asdestination address 34 the home address of MN 28; FIG. 3a alsoillustrates payload 38 and other fields 36.

In FIG. 3b, in a header according to the invention, the source address32 is the address of HA 26 and the destination address 34 is the COA ofMN 28. The header contains two new fields, 40, 42, containingrespectively identifiers (ID) for CN 24 and MN 28.

When the network is operating in FA COA as illustrated in FIG. 2a, there-addressed packet is received by the FA 30 and the MN ID 42 is used bythe FA to distinguish the different mobile nodes which aresimultaneously using that FA, and the packet is routed to MN 28.

When the re-addressed packet is received by FA 30 (for FA COA mode),FIG. 2a) or by MN 28 (for CO-COA mode, FIG. 2b), the CNID 40 is used bythe FA or the MN to recover the original source address, i.e. theaddress of the CN 24; the FA 30 or the MN 28 then re-calculates thechecksum of the packet, and delivers it to an application.

Considering now the CNID 40, this unique identifier is allocated by HA26 as soon as a packet addressed to the address of mobile is detected.The HA 26 adds an entry to an address mapping table of CNIDs and CNs,which is maintained by HA 26. Then the HA 26 sends the CNID plus the IPaddress of the correspondent CN to FA 30 (FA COA mode) or to MN 28(CO-COA mode); either a registration reply message, or a separate CNIDnotification message can be used.

When the CNID is received by FA 30 or by MN 28, an entry is added to aCNID-to-CN IP address mapping table which is maintained by the FA or MN.

Information about MNs and MN IDs is similarly exchanged.

As each packet destined for MN 28 arrives at HA 26, the HA looks up theCNID and CN address mapping table to find the CNID corresponding to thesource address on the packet; the HA then replaces the original sourceaddress with the HA address, and the destination address with the COA ofMN 28. The HA 26 adds a CNID field 40 and an MN ID field 42, adjusts thepacket checksum, and dispatches the packet.

When the packet arrives at the FA 30 or MN 28, the CNID-to-CN table islooked up and the source address of the HA 26 is replaced by the realaddress of CN 24, and the destination address is replaced with the homeaddress of the mobile. For FA COA mode, the MNID-to-MN table is lookedup, as explained above. The checksum is adjusted and the packet isdelivered to the MN 28 (for FA COA working) or to an application (forCO-COA mode).

The CNID and MNID formats can be very short and simple, so that theadditional fields do not substantially increase the header length.

The method of packet heading according to the invention for a mobile ina foreign network retains the advantage of shorter headers, and higherpayloads, in common with the invention set out in the copending patentapplication no. 99301437.2 referred to above. Since the HA address isused as the source address, the problems caused during egress filteringby using a source address different from the home network address can beavoided. Since the destination address is changed back before a packetis delivered, an application to which the packet is delivered does notneed to be reconfigured, so irritating stops and re-starts of theapplication are avoided.

A further advantage is that only the source and destination addresses ofthe header are changed; all other information is unchanged, includinginformation identifying the traffic flows from the HA 26 to the currentCOA of MN 28. It is therefore possible to adopt a standard QoSarrangement, such as RSVP, without modification to provide QoS servicesto the mobile.

A QoS session will now be described using RSVP as an example.

In FIG. 4, the CN 24 and HA 26 are associated with home network 50, andthe MN 28 and FA 30 are associated with a foreign network 52. The RSVPsession is set up as two parts, shown as Section 1 and Section 2 on theFigure; Section 1 operates between the CN 24 and the HA 26, and Section2 operates between the HA 26 and MN 28.

Section 1 is set up as a normal RSVP session in a non-mobileenvironment, with a path message sent from CN 24 to HA 26; thedifference in the inventive arrangement is that the return RESV messagefrom the HA 26 to CN 24 is not initiated until Section 2 has beencompleted.

Section 2 covers the MN 28, and is dynamically adapted as the mobilemoves from one network to another.

When HA 26 receives the PATH message from the CN 28, with the source anddestination address being the CN 24 and the home address of MN 28, theHA 26 intercepts the packet and modifies or regenerates a PATH messagevia an RSVP proxy server by re-addressing the packet as described above.The packet passes through a number of nodes or network routers, and tworouters, 54, 56 are illustrated. The PATH message is an end-to-endmessage. The proxy server can be attached to HA 26 or it can be aseparate entity.

In foreign network 52, a foreign proxy server or its equivalent in theMN 28 or FA 30, depending on the working mode, prepares a RESV messagewith the COA address of MN 28 as the source address and the HA'sdestination address; the message contains flow identificationinformation such as protocol ID as well as source/destination portnumbers, and is dispatched. The RESV message is routed hop-by-hopthrough the same servers 54, 56 as the PATH message, but in the reversedirection; the source and destination addresses for each hop are changedappropriately by the routers 54, 56.

When the RESV message is received by HA 26, or an equivalent such as ahome network proxy server, the RESV message is modified or re-generatedwith the home address of MN 28 as source address and the CN 24 asdestination address; i.e. Section 2 is completed. The RESV message ofSection 1 is now sent in conventional manner.

When the CN 24 or the home network proxy server receives the RESVmessage, a RESV confirmation message can, if requested, be sent toconfirm the whole RSVP session.

When the mode of working is FA COA, to guarantee flow-specific identity,and this class of service differentiation, for Section 2 of the RSVPsession, Port Clash avoidance control is necessary; this can be achievedby any conventional method.

I claim:
 1. A method of providing quality of service in a thirdgeneration mobile telecommunications system, in which packets areaddressed to a mobile node which has a correspondent node in a homenetwork and which is currently associated with a foreign network, saidmethod comprising the steps of: sending a quality of service enquirymessage from the correspondent node to the home network; sending saidquality of service enquiry message from the home network to the mobilenode; sending a quality of service response message from the mobile nodeto the home network by the same route as the enquiry message; andsending a quality of service response message from the home network tothe correspondent node only after receipt of the quality of serviceresponse message from the mobile node, the method comprising the furthersteps of: setting up a home agent in the home network and allocating aCare of Address in the foreign network for the mobile terminal; and inthe home network changing the header of each packet destined for themobile terminal so that the source address is the home agent address,the destination address is the Care of Address, and the header furtherincludes a correspondent node identifier code and a mobile nodeidentifier code.
 2. A method according to claim 1 in which the enquirymessage is sent by end-to-end addressing, and the response message issent by hop-to-hop addressing.
 3. A method according to claim 1 in whichthe Care of Address represents the current location of the mobile node.4. A method according to claim 3 in which when a packet arrives at theCare of Address, the destination checks the stored information andreplaces the correspondent node identifier code in the header with thecorrespondent node home address.
 5. A method according to claim 1 inwhich the Care of Address is the address of a foreign agent in theforeign network.
 6. A method according to claim 1 comprising the furthersteps of: the home agent retaining a record of correspondent node andcorrespondent node identifier codes, and the home agent sending a copyof said record to the Care of Address at which said information is alsostored.
 7. A method according to claim 6 in which, when the destinationaddress in the Care of Address is the foreign agent, the foreign agentchecks the stored information and replaces the mobile node identifiercode in the header with the mobile node home address.
 8. A methodaccording to claim 1 comprising the further steps of: the home agentretaining a record of the mobile node and mobile node identifier code;and sending a copy of said record to the Care of Address at which saidinformation is also stored.
 9. A method according to claim 1 in whichthe quality of service uses Resource reSerVation Protocol.